The overall objective of this project is to test a novel hypothesis for the pathogenesis of ulcerative colitis: we postulate that one important mechanism in the pathogenesis of ulcerative colitis is that enteric bacteria in ulcerative colitis produce factors that directly inhibit synthesis of interleukin-2 (IL-2) by lymphocytes, leading to a secondary local immunodeficiency state, and subsequent acute and chronic inflammation. In preliminary studies we have identified novel immunosuppressive factors produced by two enteric pathogens, enteropathogenic E.coli (EPEC) and enterohemorrhagic E.coli (EHEC), that profoundly inhibit IL-2 mRNA expression by activated lymphocytes and we have also isolated a cosmid clone containing the gene(s) for this factor. Therefore, the objective of this proposal is to identity these factors using molecular techniques and to determine whether patients with ulcerative colitis have enteric bacteria that produce similar immunosuppressive factors. The specific aims of the study are to: 1. Molecularly clone the factor produced by wild type EPEC strains that inhibits IL-2 mRNA expression by activated lymphocytes. 2. Isolate and characterize E.coli strains from patients with active and inactive ulcerative colitis, Crohn's disease, and control subjects and screen the isolates for the IL-2 mRNA inhibitory factor. 3. Further characterize the mechanism of action and regulatory properties of the IL-2 inhibitory factor. 4. Correlate inhibitory activity of bacterial isolates with cytokine mRNA levels in mucosal biopsies. We believe that this innovative, multidisciplinary proposal has the potential for identifying new pathogenic factors produced by intestinal bacteria in ulcerative colitis. The successful identification of such factors could lead directly to new diagnostic and therapeutic advances in this disease.